Optical waveguide mirror

Abstract: A cladding layer (2) covers a part of a substrate (1) and two core layers (8,9) are formed in the cladding layer. The two core layers merge with each other and a head (3c) of a common part of the two core layers appears on a side wall of the cladding layer. A guide portion a groove, or a pair of protrusious (4a,4b), or a recess is located near the side wall. A reflective element (5) having an end face coated with a reflective film (6a) is positioned by the guide portion so that the head of a common part of the two core layers adheres to the reflective film.

Description: This invention relates to an optical path converter, and more particularly relates to a waveguide-type optical path converter for converting a propagation direction of light using an end face reflection technique. Optical communication systems and optical signal switching systems typically include an optical modulator, optical switch and optical multiplexer/separator, etc., which are optical waveguide-type devices. Recently, research on optical wiring and the like on an optical waveguide substrate has been carried out and techniques for efficient arrangement with little loss of optical waveguide-type devices are of increasing importance. Among them, an optical path converting technique for converting a propagation direction of light is important to miniaturize apparatus which use optical devices. As an optical path conversion technique, an end face reflection technique is well known in the art. For example, this technique is disclosed in S. Valette, "State of the art of integrated technology at LETI for achieving passive optical components', Journal of Modern Optics. 1988, Vol. 35, No. 6, pp. 993-1005. The end face reflection technique has a feature that optical path conversion efficiency is high and it has a wide range of optical path conversion. In this technique, an end face of a substrate and a waveguide is ground so that an angle between a waveguide face and the end face being ground becomes 90 degrees and so that a head of the waveguide appears on a face being ground. Next, the ground face is coated with a reflective film. Referring to Fig. 1, a conventional waveguide-type optical path converter will be described. Fig. 1 shows a perspective view of the conventional converter. In Fig. 1, a silicon (Si) crystal substrate 1 is covered with a cladding layer 2, in which first and second core layers 8 and 9 are formed. The cladding layer 2 and the first and second core layers constitute two optical waveguides. The first and second core layers 8 and 9 merge with each other near one side of the cladding layer 2. An end face of a common core layer 3c is exposed by cutting the common core layer at a plane normal to the waveguides. The exposed face is ground and is covered with a reflective film 6. In addition, the other ends 3a and 3b of the first and the second core layers appear on the opposite side of the cladding layer 2. Since the cladding layer 2 has a lower refractive index than that of the core layers 8 and 9, light propagates mainly through the core layers. When light is inputted through the end surface 3a of the first core layer 8, the input light propagates mainly through the first core layer 8 to the end surface 3c of the merged or common core layer. The light is reflected at the reflective film 6. The reflected light propagates through the second core layer 9 and is outputted through the end surface 3b of the second core layer. Thus, the propagation direction of the light is changed ("converted"). Although this conventional waveguide-type optical path converter has several advantages, it nevertheless has a disadvantage in that the location at which the optical path changes direction is limited to the end face of a substrate. Therefore, it is impossible to accomplish optical path conversion at positions other than ends of a substrate. Moreover, the conventional converter has another disadvantage in that its fabrication process is complex and unsuitable for mass production because of the requirement for grinding of the waveguide end face and the coating of the waveguide end face with the reflective film one device by one device. EP-A-0 171 615 describes a hybrid optical integrated circuit and fabrication method thereof. A filter chip is inserted between guides in such a way that a predetermined angle is maintained when signal light is reflected by the filter chip and directed into an optical fiber. In view of the above it is a principal object of the present invention to provide a waveguide-type optical path converter which is not subject to any limitation as regards the position of optical path conversion and which requires no complex fabrication process. This object is achieved with the converters according to claims 1 and 2. The invention will be described in detail in connection with the drawings, in which: Figure 1 shows a perspective view of a conventional waveguide-type optical path converter; Figure 2 shows a partially exploded perspective view of an example of a waveguide-type optical path converter. Figure 3 shows a partially exploded perspective view of a first preferred embodiment of the invention; Figure 4 shows a partially exploded perspective view of another example; Figure 5 shows a partially exploded perspective view of a third example of a converter; and Figure 6 shows a partially exploded perspective view of a second preferred embodiment of the invention. Referring to Fig. 2, a first example of a converter will now be described. In Fig. 2, a cladding layer 2 covers only part of the upper planar surface of a Si crystal substrate 1, and first and second core layers 8 and 9 are formed in the cladding layer 2. The core layers 8 and 9 merge with each other near one end of the cladding layer 2. The cladding layer 2 and the first and second core layers 8 and 9 may be formed by a CVD method, a sputtering method, a flame stacking method or the like. Where the two core layers merge, a face 3c of the merged or common core layer is exposed by cutting the common core layer and the cladding layer at a plane perpendicular to the cladding layer 2 and the two core layers 8 and 9. The cutting may be performed by etching. However, the vertical exposed face does not necessarily reach the substrate 1 in the etching process. In this example, projection guides 4a and 4b are left on the substrate 1 as shown in Fig. 2. The projection guides can be fabricated simultaneously when the common core layer and the cladding layer 2 are etched. In addition, this example further includes a reflecting body 5 of square or rectangular cross section, which is fabricated so that its width matches a slot between the two projection guides 4a and 4b. An end face of the reflecting body 5 is coated with a reflective film 6a as shown in Fig. 2. The reflective body 5 is guided along the slot between projection guides 4a and 4b towards the end face 3c of the common core layer so that the reflective film 6a and the face 3c contact each other. Therefore, light propagating from the end face 3a of the first core layer toward the face 3c is reflected at the reflective film 6a and is emitted from the end face 3b. This action of optical path conversion is substantially similar to that of the conventional converter of Fig. 1. In this example, the reflecting body is preferably made of a material with the same or almost the same thermal expansion coefficient as that of the cladding layer and the core layers in order to prevent any misalignment or detachment of the reflecting film and the face 3c of the common core layer due to thermal changes. For example, when the substrate 1, the cladding layer and core layers are made of quartz-based materials, an optical fiber may be used as the reflective body 5. In this example, there is no need to locate the place for optical path conversion only at an end of the substrate 1, and optical path conversion points can be located anywhere on the substrate. Moreover, the reflective film may be made of a metal with high reflectance, such as aluminum (Al) or silver (Ag). Since reflective films on many reflective bodies can be collectively formed by an electron beam (EB) vapor-deposition method, a sputtering method or the like, this embodiment is suitable for mass production. Referring to Fig. 3, a first preferred embodiment of the invention will now be described. As shown in Fig. 3, this embodiment has a V shaped groove 7 on the substrate 1 instead of the two projection guides 4a and 4b of the first example. In addition, in this embodiment, an optical fiber 6b, one end face of which is coated with a reflective film 6a, is used as the reflective body. In this embodiment, the reflective body 6b, 6a is positioned by the V groove 7, and the reflective film 6a contacts the face 3c of the common core layer, which is an exposed face fabricated by the same process as in the first example, Formation of the V groove 7 may be accomplished by anisotropic etching of the substrate 1. For example, when the substrate 1 is made of Si crystal, the V groove 8 consisting of a (111) face is fabricated by anisotropic etching of a (100) face. This technique to couple the optical fiber 6b with the common core layer via the V groove 8 is the same as that already being used to couple an input or output optical fiber with a waveguide on a substrate via a V shaped groove (for example, see, JP-A-1-261604 (1989)). Therefore, the V groove 7 is fabricated simultaneously with V grooves for coupling optical fibers with optical waveguides on the substrate. This simplifies the fabrication process of an optical device on the substrate. In this embodiment, the substrate 1 may be made of Si, GaAs, or InP. When the substrate is made of Si, the optical waveguide may be made of a P, Ge or B doped quartz material. When a GaAs or InP substrate is used, a semiconductor-based material may be used as the waveguide materials. As an anisotropic etching liquid, a solution of KOH, KOH + alcohol, ethylenediamine + pyrocatechol or the like is used for a Si crystal substrate and a solution of HCl + H 3 PO 4 or the like for an InP substrate. For the etching mask, a material which is etched more slowly by the etching liquid than the face (100) of the substrate is used. For example, a SiO 2 thermally oxidized film, a metal film or the like is used as the etching mask material. Referring to Fig. 4, another example will now be described. In Fig. 4, the upper part of cladding layer 2 is shown removed so that the core layers 8 and 9 are exposed in order to indicate the example in detail. The second example includes a directional coupler 26, in which two optical waveguides are optically-coupled with each other, on the substrate 1. The directional coupler 26 has a length (L/2), which is a half of a full coupling length (L) of a directional coupler. Two ends of the directional coupler are connected to the core layers 8 and 9, respectively The other two ends of the directional coupler appear on a side wall of an H shaped guide hole 25, in which the reflective body 5 is inserted. The reflective body 5 is positioned by two projecting guides 24a and 24b. The exposed surface of the directional coupler on the side wall of the hole 25 is brought into contact with the reflective film 6a of the reflective body 5. Input light 41 to the core layer 8 is supplied to the point A of the directional coupler 26, proceeds over the distance (L/2) and reaches the reflective film 6a. Light reflected at the reflective film 6a proceeds over the distance (L/2), propagates into the core layer 9 and is outputted from the substrate as light 42. The combination of the directional coupler 26 with a half of the full coupling length, and the reflective film 6a of the reflective body, therefore makes an optical path conversion. While the guide hole 25 is used for holding the reflective body, a pair of projection guides 4a and 4b as in Fig. 2 may be used instead of the guide hole 25. This modification constitutes a third example, which is shown in Fig. 5. Moreover, the V groove 7 of Fig. 3 may be used instead of the guide hole 25. This modification constitutes a second preferred embodiment, which is shown in Fig. 6. As described in the above, the invention provides a waveguide-type optical path converter which is not subject to any limitation as to the position of the optical path conversion and which does not require a complex fabrication process. In the above embodiments, it will be appreciated that the location of optical path conversion is disposed not only intermediate the longitudinal sides of the substrate, as in the prior art, but also intermediate the transverse sides of the substrate.

Claims: A waveguide-type optical path converter, comprising: a substrate (1); a cladding layer (2) covering a part of a surface of the substrate (1); two core layers (8, 9) formed in said cladding layer (2) and merging with each other near a vertical wall of said cladding layer (2), wherein a merged head portion (3c) of said two core layers (8, 9) appears on said vertical wall of said cladding layer (2); a reflective body (6b) having an end face coated with a reflective film (6a); and guide means (7) located on the substrate (1) for positioning the reflective body (6b) so that the reflective film (6a) contacts said merged head portion (3c) of said two core layers (8,9), characterized in that said reflective body (6b) is a segment of an optical fiber, in that said reflective film is made of a metal with high reflectance; and in that said guide means is a groove (7) formed on said substrate (1). A waveguide-type optical path converter, comprising: a substrate (1); a cladding layer (2) covering a part of a surface of said substrate (1); two core layers (8, 9) formed in said cladding layer (2); a directional coupler (26) having two ends connected to said two core layers (8, 9), respectively, and a length which is a half of a full coupling length, for optically coupling the two core layers (8, 9) with each other; a reflective body (6b) having an end face coated with a reflective film (6a); wherein said reflective body (6b) is a segment of an optical fiber, said reflective film (6a) is made of a metal with high reflectance, and guide means are located on the substrate (1) for positioning said reflective body (6b) so that said reflective film contacts the opposite two ends of said directional coupler (26), wherein said guide means is a groove (7) formed on said substrate (1).

Inventors: KITAMURA NAOKI, NISHIMOTO HIROSHI, KITAMURA, NAOKI, NISHIMOTO, HIROSHI, KITAMURA, NAOKI, C/O NEC CORPORATION, NISHIMOTO, HIROSHI, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1994
Main classification: G02B6
IPC codes: G02B6